• International Journal of High-Rise Buildings
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• v.7 no.4
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• pp.375-387
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• 2018

This paper presents a review on progressive collapse mechanism of steel framed buildings exposed to fire. The influence of load ratios, strength of structural members (beam, column, slab, connection), fire scenarios, bracing systems, fire protections on the collapse mode and collapse time of structures is comprehensively reviewed. It is found that the key influencing factors include load ratio, fire scenario, bracing layout and fire protection. The application of strong beams, high load ratios, multi-compartment fires will lead to global downward collapse which is undesirable. The catenary action in beams and tensile membrane action in slabs contribute to the enhancement of structural collapse resistance, leading to a ductile collapse mechanism. It is recommended to increase the reinforcement ratio in the sagging and hogging region of slabs to not only enhance the tensile membrane action in the slab, but to prevent the failure of beam-to-column connections. It is also found that a frame may collapse in the cooling phase of compartment fires or under travelling fires. This is because that the steel members may experience maximum temperatures and maximum displacements under these two fire scenarios. An edge bay fire is more prone to induce the collapse of structures than a central bay fire. The progressive collapse of buildings can be effectively prevented by using bracing systems and fire protections. A combination of horizontal and vertical bracing systems as well as increasing the strength and stiffness of bracing members is recommended to enhance the collapse resistance. A protected frame dose not collapse immediately after the local failure but experiences a relatively long withstanding period of at least 60 mins. It is suggested to use three-dimensional models for accurate predictions of whether, when and how a structure collapses under various fire scenarios.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.41 no.3
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• pp.201-208
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• 2021

In this paper, the effect on the lateral and torsional behavior of ballastless railway plate girder bridge by the installation of the lower horizontal bracing has been reviewed. First of all, the most efficient lower bracing arrangement has been reviewed by comparing and examining the lateral displacement due to the train load, targeting analysis models with different arrangement types of lower bracing. Next, the research on torsional behavior of plate girder bridge with lower bracing has been conducted. In addition, the torsion constant from FEM analysis results has been compared with the torsion constant of a railroad plate girder bridge with a closed section by substituting the upper and lower horizontal bracing with equivalent thickness. Based on this comparison, the impact on the bridge span length and the cross section area of the lower bracing has been examined. Through this study, the curve graph related to lateral buckling moment and torsional constant ratio is presented and the range of plate girder bridge requiring torsional reinforcement is proposed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2010.05a
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• pp.580-581
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• 2010

• Journal of the Korean Society for Precision Engineering
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• v.22 no.11 s.176
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• pp.7-15
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• 2005

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.10a
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• pp.374-375
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• 2012

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.3
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• pp.875-888
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• 2013

The researches have recently progressed toward the use of the superelastic shape memory alloys (SMAs) to develop new smart control systems that reduce permanent deformation occurring due to severe earthquake events and that automatically recover original configuration. The superelastic SMA materials are unique metallic alloys that can return to undeformed shape without additional heat treatments only after the removal of applied loads. Once the superelastic SMA materials are thus installed at the place where large deformations are likely to intensively occur, the structural system can make the best use of recentering capabilities. Therefore, this study is intended to propose new buckling-restrained braced frames (BRBFs) with superelastic SMA bracing systems. In order to verify the performance of such bracing systems, 6-story braced frame buildings were designed in accordance with the current design specifications and then nonlinear dynamic analyses were performed at 2D frame model by using seismic hazard ground motions. Based on the analysis results, BRBFs with innovative SMA bracing systems are compared to those with conventional steel bracing systems in terms of peak and residual inter-story drifts. Finally, the analysis results show that new SMA bracing systems are very effective to reduce the residual inter-story drifts.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.6
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• pp.632-638
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• 2014

Nowadays, as part of an effort to increase the efficiency of propulsion shafting system, the revolution of the main diesel engine in CMCR(Contract Maximum Continuous Rating) is reduced whereas the stiffness of hull structure supporting the main diesel engine is relatively flexible. However, vibration problems related with resonant response of main diesel engine are increasing although top bracing is installed between the main diesel engine and the hull structures to increase natural frequency of engine body above CMCR to avoid resonant phenomenon. In this study, the dynamic characteristic of top bracing is reviewed by analyzing measuring results of general cargo ships which apply the hydraulic type instead of the friction type to control the natural frequency and the vibration of the engine body. Moreover, considering the vibration characteristic of the engine body and the hydraulic type of the top bracing by varying the number of top bracing, authors suggest the more effective way to control the vibration of the engine body despite of lower stiffness of the hull structure than in the past when the hydraulic type of top bracing is used.

• Steel and Composite Structures
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• v.18 no.1
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• pp.165-185
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• 2015

The suspended zipper bracing system is suggested to reduce the flaws of ordinary zipper braced and concentric inverted V braced frames. In the design procedure of suspended zipper bracing systems, columns and top story truss elements are strengthened. This bracing system show different performances and characteristics compared with inverted V braced and ordinary zipper frames. As a result, a different response modification factor for suspend zipper frames is needed. In this research paper, the response modification factor of suspended zipper frames was obtained using the incremental dynamic analysis. Suspended zipper braced frames with different stories and bay lengths were selected to be representations of the design space. To analyze the frames, a number of models were constructed and calibrated using experimental data. These archetype models were subjected to 44 earthquake records of the FEMA-P695 project data set. The incremental dynamic analysis and elastic dynamic analysis were carried out to determine the yield base shear value and elastic base shear value of archetype models using the OpenSEES software. The seismic response modification factor for each frame was calculated separately and the values of 9.5 and 13.6 were recommended for ultimate limit state and allowable stress design methods, respectively.

• Journal of the Earthquake Engineering Society of Korea
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• v.18 no.3
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• pp.133-140
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• 2014

The friction damper can be used for improving the seismic resistance of existing buildings. The damper is often installed in bracing members. The energy dissipation capacity of the damping systems depends on the type of the structure, the configuration of the bracing members, and the property of dampers. In Korea, there are numerous low- to mid-rise reinforced concrete moment frames that were constructed considering only gravity loads. Those frames may be vulnerable for future earthquakes. To resolve the problem, this study developed a toggle bracing system with a high density friction damper. To investigate the improvement of reinforced concrete frames after retrofit using the developed damped system, experimental tests were conducted on frame specimens with and without the damped system. The results showed that the maximum strength, initial stiffness and energy dissipation capacity of the framed with the damped system were much larger than those of the frame without the damped system.

• Journal of the Korean Geotechnical Society
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• v.15 no.1
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• pp.31-40
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• 1999

The bracing system using screw jack is not effective for the restraining of adjacent ground displacement. since the screw jack dose not induce sufficient preloading on struts. In order to protect excessive displacement of adjacent ground at braced excavation, new preloading jack was developed in the country. In this paper, the new preloading jack and the measurement results of the lateral displacement of braced wall at three deep excavation sites in Seoul city are introduced. The measurement results showed that the maximum displacements of braced wall are smaller than 0.15% of excavation depth, therefore the wall displacements can be minimized by preloading which is acted on bracing. If the bracing system with new preloading jack is used in braced excavation, it is effective for reducing the cost and period of construction.